JPH05188767A - Developing device - Google Patents

Abstract

PURPOSE:To provide the developing device where deterioration of developer due to residue developer in the vicinity of a developer layer thickness restriction means is prevented when a two components developer is utilized and where an image of the same good quality as an initial image can be formed over a long period of time. CONSTITUTION:In the developing device 30 provided with a developer carrier 31 carrying the two components developer T consisting of toner and magnetic carrier and a developer thickness restriction means 33 restricting the developer T on the developer carrier 31 to be a thin layer, the quantity of the residue developer TD at the upstream of the carrying direction of the developer carrier 31 at the side of the developer layer thickness restriction means 33 is made less than 1/3 of the whole quantity of developer T. Therefore, the toner inside the developer T carried by the developer carrier 31 does not receive a great pressurizing force due to the residue developer TD and is not easily deteriorated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for an image forming apparatus such as a copying machine or a laser beam printer (LBP) using an electrophotographic method or an electrostatic recording method.

[0002]

2. Description of the Related Art Conventionally, as a developing method using a developing device, a one-component system using a one-component developer has been widely used. A typical one-component system is a one-component jumping developing method using a magnetic toner, but this developing method has a disadvantage that a proper color image cannot be formed because the toner contains a magnetic material. Although a proper color image can be formed by the one-component developing method using a non-magnetic toner, it is not easy to attach the toner on the developer carrying member, and the stability and durability of the image are problematic. There is.

On the other hand, in the two-component developing method using a toner and a magnetic carrier, since a non-magnetic toner can be used, a high quality color image can be formed and the toner is made to adhere to the carrier. Therefore, the adhesion of this developer on the developer carrying member is also facilitated via magnetic force or the like. Therefore, a two-component developing method is often used in a developing device that forms a color image other than black and white.

FIG. 1 shows an example of a developing device 30 using a magnetic brush developing method which is one of the two-component developing methods. In the developing device 30, a two-component developer T composed of a non-magnetic resin toner and a magnetic carrier in a developing device main body 36 is provided on a peripheral surface of a developing sleeve 31 as a developer carrying member, and a magnet roller 3 is provided.
The developer is attracted by the action of the magnetic force of 2, and the developer is moved to the side of the photosensitive drum 1 which is an image carrier with the rotation of the developing sleeve 31, and the spikes of the developer T are formed on the surface facing the photosensitive drum 1. Then, only the toner is supplied to the latent image on the photosensitive drum 1. In this case, a developing blade 33 serving as the developer layer thickness regulating member is arranged above the developing sleeve 31, and the developing blade 33 causes the developing sleeve 31 to move.
The layer thickness of the developer T adsorbed on the photosensitive drum 1 and moving to the photosensitive drum 1 side is regulated to a constant thin layer.

[0005]

However, in the developing device 30, a large amount of the developer T regulated by the developing blade 31 is accumulated beside the developing blade 33 as the staying developer TD, and the staying developer TD is retained. However, a large pressure is applied to the developer T on the developing sleeve 31 that is successively conveyed to the developing blade 33 side. Therefore, a large force is applied between the magnetic carrier and the resin toner, and SiO ₂ or Ti externally added to the resin toner in order to improve the fluidity and the like.
There is a disadvantage that fine particles such as O ₂ are embedded in the resin toner and the function cannot be exhibited.

Further, since the toner itself is also sharpened by the collision with the carrier and becomes rounded as a whole, the mechanical adhesion of the toner to the carrier and the photosensitive drum 1 is increased, and the development and the development corresponding to the electric field are performed. The transfer cannot be performed sufficiently. Therefore, if an image is formed with such a developer,
In the low density portion, for example, when a copying machine or the like is used (so-called analog latent image), density unevenness occurs, and when a laser beam printer or the like is used (so-called digital latent image)
Image defects such as missing dots and non-uniform dot area are generated, and image defects such as density reduction and density unevenness due to transfer defects occur at high density portions.

The present invention has been made in view of the above problems. An object of the present invention is, when a two-component developer is used, the development caused by the retention of the developer near the developer layer thickness controlling means. Another object of the present invention is to provide a developing device capable of preventing deterioration of the agent and forming a good image similar to the initial image for a long period of time.

[0008]

In order to achieve the above-mentioned object, the present invention provides a developer carrier for carrying a two-component developer comprising a toner and a magnetic carrier, and a thin developer on the developer carrier. In a developing device having a developer layer thickness regulating means for regulating the layers, the amount of the developer staying on the upstream side of the developer carrier in the developer carrying direction next to the developer layer thickness regulating means is defined as the total amount of the developer. It is characterized by being set to 1/3 or less of.

[0009]

In a developing device using a two-component developer consisting of toner and carrier, the developer is supported on the developer carrier by the influence of the pressure of the retained developer generated on one side of the developer layer thickness regulating member. This causes deterioration and the like of the toner in the moving developer and causes various harmful effects.

Therefore, the amount of the staying developer is suppressed to 1/3 or less of the total amount of the developer in the developing device so that the adverse effect of pressurizing the staying developer does not occur. The value of 1/3 was calculated by experiments.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First, a first embodiment of this embodiment will be described with reference to FIGS.

FIG. 2 shows a cross section of a copying machine capable of forming a full-color image (the maximum transfer material size capable of forming an image is A4 lateral size). In FIG. 2, 1 is an image carrier rotated in the direction of the arrow. It is a photosensitive drum (electrophotographic photosensitive member). A primary charging device 2, a rotary developing device 3, a transfer device 4, and a cleaning device 5 are arranged around the photosensitive drum 1.
A sheet feeding cassette 5, a sheet feeding roller 6, a registration roller 7 and the like are provided on the sheet feeding side of the transfer device 4, and a separation claw 8, a conveying section 9, a fixing device 10, a sheet discharging tray 11 and the like are provided on the sheet discharging side. Are arranged. A transparent platen 12 on which the document K is placed is disposed above the apparatus body above the photosensitive drum 1 and the like, and below the platen 12, a moving lamp 13, a moving mirror 14, fixed mirrors 15 and 16 are provided. , 17, imaging lens 1
8. An image reading and exposing section including a color separation filter 19 and the like is provided.

The rotary developing device 3 has four developing devices 30, that is, cyan, magenta, yellow and black developing devices each having cyan, magenta, yellow and black toners in a rotation supporting member 3b which rotates around a support shaft 3a. Bowl 3
0C, 30M, 30Y, 30B are provided so that a predetermined developing device 30 can be positioned laterally of the photosensitive drum 1 based on image information of a predetermined color.

The transfer device 4 positions and holds the transfer material P on the outer peripheral surface of the transfer drum 4a via a gripper 4b or the like, and when the transfer drum 4a rotates, the transfer material P is exposed on the transfer material P close to one side of the photosensitive drum 1. The toner image on the drum 1 is transferred.

The image reading / exposure unit irradiates the image of the document K on the platen 12 with the moving lamp 13, and the reflected image light L is exposed through the moving mirror 14, fixed mirrors 15, 16, 17 and the imaging lens 18. Since the image light L is exposed on the drum 1 and passes through the color separation filter 19 upon the exposure, only the image light L based on predetermined image information is exposed on the photosensitive drum 1.

That is, when the image light L based on, for example, magenta image information is exposed on the photosensitive drum 1 uniformly charged by the primary charger 2 through the image reading and exposing section, the photosensitive drum 1 is exposed. An electrostatic latent image is formed. The electrostatic latent image is directed toward the pre-positioned magenta developing device 30M of the rotary developing device 3 as the photosensitive drum 1 rotates, and magenta toner is supplied by the magenta developing device 30M to visualize it as a toner image. Then, the toner image is transferred onto the transfer material P on the transfer drum 4a.

After the transfer of the photosensitive drum 1 is completed, the residual toner is cleaned by the cleaning device 5, and then the primary charging device 2 again uniformly charges the photosensitive drum 1 to obtain cyan image information through the image reading and exposing section. The image light L based on the light is exposed to form an electrostatic latent image on the photosensitive drum 1. Then, this electrostatic latent image is visualized as a toner image by supplying cyan toner by a cyan developing device 30C, and the toner image is transferred onto the transfer material P on the transfer drum 4a in an overlapping manner. Similarly, the toner images by the yellow and black developing units 30Y and 30B based on the yellow and black image information are transferred onto the transfer material P in an overlapping manner.

On the other hand, the transfer material P in the paper feed cassette 5 is taken out one by one by the paper feed roller 6 and then sent to the registration roller 7, and the transfer roller 4 of the transfer device 4 is timed by the registration roller 7. And is positioned and held on the transfer drum 4a of the transfer device 4 via a gripper 4b and the like. Then, as the transfer drum 4 a rotates, the transfer material P on which the toner images of the four colors described above are transferred and transferred is separated from the transfer drum 4 a via the separation claw 8 and is transferred to the fixing device 10 via the transport unit 9. Sent to. And this fixing device 1
The transfer material P in which the toner image is dissolved and mixed by 0 and fixed as a full-color image is stacked on the paper discharge tray 11, and a series of image forming operations is completed.

The developing device 30 in the rotary developing device 3 will be described in more detail with reference to FIG. The developing device 30 uses a two-component developer T composed of a non-magnetic resin toner suitable for color images and a magnetic carrier, and supplies the toner to the photosensitive drum 1 by a magnetic brush developing method. A developing sleeve 31 as a developer carrier, a magnet roller 32 as a magnetic field generating means, a developing blade 33 as a developer layer thickness regulating means, and first and second screws 34, 35 as agitating and conveying means for the developer. And a developing device main body 36 that holds the developer T and the like.

The developing sleeve 31 is close to the photosensitive drum 1 on the surface of the developing device main body 36 facing the photosensitive drum 1 (in this embodiment, the gap between the photosensitive drum 1 and the developing sleeve 31 is 800 μm). ) Is provided and has a cylindrical shape that is driven to rotate in the direction of the arrow in the figure by a drive source (not shown), and holds the developer T in the developing device main body 36 on its outer peripheral surface by the action of the magnet roller 32 inside. At the same time, the toner in the developer T is supplied to the photosensitive drum 1 side. The toner and the carrier that have not been supplied to the photosensitive drum 1 side are returned to the developing device main body 36 again.

The magnet roller 32 is the developing sleeve 31.
It is arranged in a fixed state inside and has five magnetic poles S on its outer peripheral surface.
1, S2, N1, N2, N3. The developing sleeve 31 draws the developer T to the outer peripheral surface thereof at the position of the drawing magnetic pole N2, and the developing sleeve 31 releases the developer T on the outer peripheral surface thereof to the developing device main body 36 side at the position of the discharging magnetic pole N3. , A developing magnetic pole S that opposes the photosensitive drum 1.
At the position 1, the ears of the developer T are formed on the outer peripheral surface of the developing sleeve 31. The magnetic poles N1 and S2 are magnetic poles for carrying the developer T.

The developing blade 33 is arranged above the developing sleeve 31 so as to have a certain gap (in this embodiment, the gap is 500 μm) with the developing sleeve 31, and the developing agent attracted to the outer peripheral surface of the developing sleeve 31. The layer thickness of the agent T is regulated to a certain thin layer, the developer T in the thin layer is moved to the photosensitive drum 1 side, and the toner in the developer T is also triboelectrically charged.

The first and second screws 34 and 35 are arranged on both sides of a partition 37 at the bottom of the developing device main body 36, and the rotation of the developer T moves the developer T above and below the plane of FIG. The developer T in the container body 36 is agitated and conveyed (circulation).
At the same time, it has a function of sufficiently triboelectrically charging the toner in the developer T. In particular, the first and second screws 35 and 36 sufficiently stir the newly replenished toner and the developer T whose toner has been consumed and the density of which has been reduced to sufficiently agitate the developer T.
It has a role of maintaining the toner concentration in the inside at a uniform predetermined value.

Here, the toner is not only colored resin particles (containing a binder resin, a coloring material and, if necessary, other additives), but also hydrophobic colloidal silica (SiO ₂ ) and Ti.
Colored resin particles to which fine powders such as O ₂ (these are those for improving the fluidity of the toner) are externally added. Particularly, in this embodiment, as the developer T, a toner having a negative charge characteristic of a polyester resin having a volume average particle diameter of 8 μm and a carrier having a volume average particle diameter of 50 μm are used.

That is, the developer T scooped up on the developing sleeve 31 at the position of the scooping magnetic pole N2 of the magnet roller 32 is moved toward the developing blade 33 as the developing sleeve 31 rotates, and the developing blade 33 causes the developer T to move. The layer thickness is restricted to a constant thin layer. After that, the developer T on the developing sleeve 31 regulated to the thin layer is moved toward the photosensitive drum 1 and forms a spike at the position of the developing magnetic pole S1 of the magnet roller 32, but is applied to the developing sleeve 31. Due to the action of the developing bias voltage, only the toner in the bristles flies to the electrostatic latent image side of the photosensitive drum 1 to form a toner image. Then, the remaining toner and carrier are moved into the main body 36 of the developing device as the developing sleeve 31 is rotated, and are dropped to the first and second screws 34, 35 side at the position of the discharge magnetic pole N3 of the magnet roller 32. Then, the developer T having the lowered toner concentration is sufficiently agitated with the toner newly supplied by the first and second screws 34 and 35, and is pumped up to the developing sleeve 31 again.

Here, the developing bias voltage is a superposition of an AC voltage (in the present embodiment, a peak-to-peak voltage Vpp of 2000 V and a frequency f of 2000 Hz) and a DC voltage. Incidentally, in the two-component developing method, if a developing bias voltage having an AC component is applied, the developing efficiency is increased,
Images tend to be of high quality.

If the developing device 30 as described above is used for a long period of time, as described in the section of the prior art, the staying developer TD which is regulated and accumulated beside the developing blade 33. Due to the influence of
The developer T, which is attracted to the circumference of one and is successively conveyed toward the developing blade 33, receives pressure, deteriorates the toner, and causes various harmful effects such as an image defect. In this case, if the amount of the staying developer TD is reduced, coating failure of the developer T on the developing sleeve 31 may occur. Therefore, tests as shown in Tables 1 and 2 were conducted in order to define the optimum amount of the retained developer TD that does not deteriorate the toner and does not cause coating defects on the developing sleeve 31.

In Table 1, 600 g of the developer is placed in the developing device 30.
(Total amount of developer) When the amount of staying developer TD was changed in various cases, the state of the image after the image was formed on 10,000 sheets of the transfer material P was observed. , × indicates that the image is defective, Δ indicates that there is some defective portion of the image, and ○ indicates that the image is good. Table 1
If the staying developer TD is 50 g, the developing sleeve 31
However, when the amount of staying developer TD is 100 to 200 g, the amount of staying developer TD is 1/3 or less of the total amount of developer T. in the case of)
A good image was obtained. This is because the effect of pressing the developer T by the staying developer TD is reduced, and it is considered that the deterioration of the toner is unlikely to proceed.

Table 2 shows that the amount of the staying developer TD is fixed at 150 g and the amount of the developer T other than the staying developer TD in the developing device 30 is variously changed and 10,000 transfer materials P are transferred. Table 1 shows the state of the image after the image was formed on it.
Similar to the case of, the symbol x indicates that the image is defective, the symbol Δ indicates that the image is slightly defective, and the symbol ◯ indicates that the image is favorable. From Table 2, a good image was obtained when the amount of the developer other than the staying developer TD was 300 g or more (when the amount of the staying developer TD was 1/3 or less of the total developer T). This is because when the amount of the developer T other than the staying developer TD is small, the staying developer TD and the other developer T are not sufficiently replaced with each other, which causes an image defect.

Similarly, when the amount of the staying developer TD is fixed at 200 g, the amount of the developer T other than the staying developer TD is 4
00g or more (the amount of stagnant developer TD is 1 / of the total amount of developer T)
3 or less), a good image was obtained. Further, as a result of the similar test, when the amount of the staying developer TD is finally 1/3 or less of the amount of all the developer T in the developer 30, the developing blade 33
It was found that pressurization of the developer T by the staying developer TD on the side of the toner was prevented, deterioration of the toner was prevented, and a good initial image could be maintained for a long period of time. In the developing device 30 according to the present embodiment, the total amount of the developer T is 400
Stable developer T on the developing sleeve 33 when g or more
I found that I could pump up.

Here, the amount of staying developer TD is changed to the total developer T.
In order to reduce the amount to 1/3 or less, a method of adjusting the magnetic force of the magnetic pole S2 of the magnet roller 32 on the side of the developing blade 33, or a method of enclosing a portion of the staying developer TD described later with a constant developer holding frame Etc.

[0033]

[Table 1]

[0034]

[Table 2] Next, a second embodiment of the present invention will be described with reference to FIG. still,
Components having the same functions as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

This embodiment relates to the developing device 30 in which the magnet roller 32 'in the developing sleeve 31 rotates in the direction opposite to the developing sleeve 31. A carrier return member 38 is provided on one side of the developing blade 33 above the developing sleeve 31.
Is provided, and a predetermined amount of the retained developer TD regulated by the developing blade 33 is retained below the carrier return member 38. The magnet roller 32 'is provided with, for example, eight magnetic poles N and S.

Even in the developing device 30 described above, when an image is formed by using the same two-component developer T as the developer T according to the first embodiment, the amount of the total developer T is 800 g and the residual development is performed. When the amount of the developer TD is 200 g (the amount of the staying developer TD is 1/3 or less of the amount of the total developer T), the toner deterioration due to the staying developer TD does not occur and the same as in the first embodiment. In addition, an image similar to the initial image could be stably formed over a long period of time.

Next, a third embodiment of the present invention will be described with reference to FIG. It should be noted that components having the same functions as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, a carrier return member 39 for restricting the amount of staying developer TD is arranged beside the developing blade 33 above the developing sleeve 31 in the developing device main body 36. The staying developer TD is held in a space S surrounded by the recess 39a and the developing sleeve 31, and the staying developer TD in the space S is stored with respect to the total developer T amount 600 g in the developing device 30. Is 150 g (the amount of staying developer TD is 1/3 of the total amount of developer T).
The following). The magnetic pole N1 of the magnet roller 32 is a developing magnetic pole, the magnetic pole N3 is a scooping magnetic pole, and a magnetic pole S.
Reference numeral 3 is an emission magnetic pole, and magnetic poles N2, S1 and S2 are carrier magnetic poles.

When an image is formed by the above-described developing device 30 using the same two-component developer T as the developer T according to the first embodiment, the toner is not deteriorated due to the stagnant developer TD. Similar to Example 1, a good image similar to the initial image could be stably formed over a long period of time. In particular, in this embodiment, the amount of staying developer TD can be determined by the space S formed by the carrier return member 39 and the like, so that the magnetic pole of the magnet roller 32 (particularly the magnetic pole N).
2) It is possible to eliminate variations in the amount of staying developer TD due to variations in magnetic force, and it is possible to always set the amount of staying developer TD to a constant value.

In the above first and second embodiments, the developing device used for a copying machine or the like (what develops a so-called digital latent image on a photosensitive drum) has been described, but the present invention is not limited to this and a high quality laser is used. Of course, the present invention can be applied to the developing device 30 used for a beam printer or the like (what develops an analog latent image on a photosensitive drum). In particular, in a developing device that develops a laser pulse width-modulated latent image (dot latent image formed by modulating the number of pulses per pixel corresponding to an image density value) among digital latent images, high image quality is obtained. Image defects are easily noticeable, and the effect of the present invention on such a developing device is great.

Further, the developing method using the two-component developer is not limited to the magnetic brush developing method shown in the first embodiment, and it goes without saying that a two-component jumping developing method or the like may be used. is there. Further, although the non-magnetic toner has been described in the first to third embodiments, it goes without saying that it may be a magnetic toner.

[0042]

As is apparent from the above description, according to the present invention, when a two-component developer is used, the amount of staying developer is suppressed to 1/3 or less of the total amount of developer. For,
Deterioration of toner in the developer due to stagnant developer is prevented,
With this developing device, a good image similar to the initial image can be formed over a long period of time.

[Brief description of drawings]

FIG. 1 is a sectional view of a developing device according to a first embodiment.

FIG. 2 is a side sectional view of an image forming apparatus including the developing device.

FIG. 3 is a sectional view of a developing device according to a second embodiment.

FIG. 4 is a sectional view of a developing device according to a third embodiment.

[Explanation of symbols]

 31 developing sleeve (developer carrying member) 33 developing blade (developer layer thickness regulating means) T developer TD stagnant developer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kazuhisa Kenmochi 3-30-2 Shimomaruko Ota-ku, Tokyo Canon Inc. (72) Hiroyuki Suzuki 3-30-2 Shimomaruko Ota-ku, Tokyo Canon Inc. Within the corporation

Claims (5)

[Claims] 1. Development comprising a developer carrying member for carrying a two-component developer comprising a toner and a magnetic carrier, and a developer layer thickness controlling means for restricting the developer on the developer carrying member to a thin layer. In the device, the amount of the developer staying upstream of the developer carrier in the developer carrying direction next to the developer layer thickness regulating means is set to 1/3 or less of the total amount of the developer. .. 2. When the developer carrier is suitable for forming an image on a transfer material having a length of A4 longitudinal size or more, the total amount of the developer is 400 g or more. The developing device according to claim 1. 3. The developing device according to claim 1, wherein the toner contains polyester as a main component. 4. The developing device according to claim 1, wherein fine particles such as SiO ₂ and TiO ₂ are externally added to the toner. 5. The latent image on the image carrier to which the toner is supplied from the developer carrier is a dot latent image formed by modulating the number of pulses per pixel corresponding to the image density value. The developing device according to claim 1, 2, 3, or 4.